This propulsion is used for small boats and is said to be more efficient than a propeller.
The magenta arrow indicates the direction of the boat's movement.
The blue arrow represents the force exerted by water on the pink foil.
The foil moves up and down thanks to an eccentric slider crank mechanism consisting of the input green crankshaft and yellow conrods.
Here the slider is replaced with the red roller that rolls along the runway of four rods.
Such an arrangement allows the foil to rotate a limited angle thereby creating the angle of attack of the foil. The rectangular protrusions at the lower ends of the conrods determine the value of the attack angle.
Reversing the input rotation does not cause the boat to move backward. So use the rudder to get that.

Inventor files of this video:
https://www.mediafire.com/file/6zbls2...